A vacuum cleaner typically comprises a main body containing dirt and dust separating apparatus, a cleaner head connected to the main body and having a suction opening, and a motor-driven fan unit for drawing dirt-bearing air through the suction opening. The suction opening is directed downwardly to face the floor surface to be cleaned. The dirt-bearing air is conveyed to the separating apparatus so that dirt and dust can be separated from the air before the air is expelled to the atmosphere. The separating apparatus can take the form of a filter, a filter bag or, as is known, a cyclonic arrangement. The present invention is not concerned with the nature of the separating apparatus and is therefore applicable to vacuum cleaners utilizing any of the above arrangements or another suitable separating apparatus.
A driven agitator, usually in the form of a brush bar, is supported in the cleaner head so as to protrude by a small extent from the suction opening. The brush bar is activated mainly when the vacuum cleaner is used to clean carpeted surfaces. The brush bar comprises an elongate cylindrical core bearing bristles which extend radially outward from the core. Rotation of the brush bar may be driven by an electric motor powered by a power supply derived from the main body of the cleaner. The rotation of the brush bar causes the bristles to sweep along the surface of the carpet to be cleaned to loosen dirt and dust, and pick up debris. The suction of air generated by the fan unit of the vacuum cleaner causes air to flow underneath the cleaner head and around the brush bar to help lift the dirt and dust from the surface of the carpet and then carry it from the suction opening through the cleaner head towards the separating apparatus.
When the cleaner head is to be used to clean a hard floor surface, it is desirable to stop the rotation of the cleaner head to prevent the floor surface from becoming scratched or otherwise marked by the moving bristles of the brush bar. For this purpose, a switch may be provided on the cleaner head to enable a user to de-activate the motor driving the rotation of the brush bar before the cleaner head is moved on to the hard floor surface. Alternatively, a sensor may be provided on the bottom surface of the cleaner head for detecting the type of floor surface upon which the cleaner head has been located, and for deactivating the motor depending on the detected type of floor surface.
A plurality of wheels may be provided on the bottom surface of the cleaner head both to facilitate the manoeuvring of the cleaner head over the hard floor surface and to raise the bottom surface of the cleaner head above the floor surface, thereby preventing the floor surface from becoming marked through contact with the bottom surface of the cleaner head. This raises the suction opening of the cleaner head above the hard floor surface, typically so that it is substantially parallel with that surface.
When the cleaner head is moved on to the hard floor surface, the continued suction of air into the suction opening of the cleaner head enables debris to be lifted from the hard floor surface and into the cleaner head. However, because the brush bar is not rotating the hard floor surface is not agitated by the cleaner hard, with the result that some dust and relatively fine dirt can remain on the hard floor surface.
The suction of air through the suction opening creates a pressure difference between the air passing through the cleaner head and the external environment. The raising of the suction opening of the cleaner head above the hard floor surface means that no seal is formed between the periphery of the suction opening and the floor surface. This in turn means that the pressure difference between the air passing through the cleaner head and the external environment will be relatively low, which has the result of a relatively poor entrainment within the airflow entering the cleaner head of dirt and dust located in crevices in the hard floor surface.